It is a shore thing.

For certain, you will find this crab in Vineyard waters, and once you know more, you will be even surer that you don’t want it here.

The Asian shore crab crawls innocently enough along pond bottoms and in near-shore ocean water. This is no intentional invader. It came unseen and inadvertently, likely in the ballast water of large international ships. This crab’s larval stage is planktonic, or free-floating, and easily could have drifted to our shores after expulsion from a ship after a long sea voyage.

This crab hails from the Pacific Ocean and is found off Russia, down along the coasts of China and Korea, and around the islands of Japan. In North America, it was first found on our coast in my home state of New Jersey — Cape May to be exact — in 1988. This invasive crab has since moved both north and south from its original harbor landing. The Asian shore crab is now reportedly found from North Carolina to Maine, and may continue to spread.

Asian shore crabs are distinct and easy to identify for any observant beachcomber. They are small, their carapace (shell) reaching only about 1.5 inches in diameter, about the size of a silver dollar. Their color can vary: They can appear green, purple, orange, brown or red. But the shape of their shell and its distinct details give them away. Their shell is squarish and has three spines on each side. Contrast that to another invading imposter, the green crab, which has five spines on each side of its shell. To confirm, note the light and dark bands on the Asian shore crab’s legs.

While many animals don’t mind sharing habitat, this small but mighty monster does. It has not made many friends. In fact, it is a crab to be feared and despised.

Asian shore crabs threaten our native crabs and other marine life. They can outcompete and outhunt the locals. Add to that a very long and amazingly efficient breeding season, and it all spells serious trouble for the native species — not just other crabs, but anything going after the same foods. The breeding season for the Asian shore crab is twice as long as most native crabs’, and each female can produce up to 50,000 eggs, three to four times a season!

Scientists say that Asian shore crabs “overwhelm and dominate” their habitat and have few predators here — which is one more advantage they have over their local competitors. Humans, for instance, find them inedible. Connoisseurs of these crabs include gulls, striped killifish and rockfish.

Asian shore crabs, though, are omnivores and will eat almost anything. Luckily, some natives are fighting back. Mussels are a favorite food for these crabs, and over time are developing harder shells that resist the advances of the shore crab. Hopefully you can’t teach an old crab new tricks.

For now, unfortunately, we are limited in our response to this seaside strongman. I do my part and remove them from the water every chance I get. (Remember: squarish shell and three spines on each side.) Though it may seem cruel, all is fair in love, war and invasive species management.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.